1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of hydrocarbons. More specifically, the invention relates to a process for separating isoprene from a feed mixture of isoprene and at least one additional C.sub.4 or C.sub.5 hydrocarbon, which process employs a particular adsorbent to selectively adsorb isoprene from the feed mixture.
2. Background Information
The use of crystalline aluminosilicates to perform hydrocarbon separation is well known in the separation art. Examples of such separations are disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491 wherein a type A zeolite is used to separate normal paraffins from branched chain paraffins. The use of faujasites to separate olefinic hydrocarbons from paraffinic hydrocarbons is described in U.S. Pat. Nos. 3,265,750 and 3,510,423. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the zeolitic adsorbent, while excluding the larger or branched chain molecules.
In addition to being used in processes for separating hydrocarbon types, adsorbents comprising type X or Y zeolites have also been employed in processes to separate individual hydrocarbon isomers. In the processes described, for example, in U.S. Pat. Nos. 3,626,020 to Neuzil, 3,663,638 to Neuzil, 3,665,046 to deRosset, 3,668,266 to Chen et al., 3,686,343 to Bearden Jr. et al., 3,700,744 to Berger et al., 3,734,974 to Neuzil, 3,894,109 to Rosback, 3,997,620 to Neuzil and B426,274 to Hedge, particular zeolitic adsorbents are used to separate the para isomer of bialkyl substituted monocyclic aromatics from the other isomers, particularly para-xylene from other xylene isomers.
Other adsorptive separation art deals specifically with the separation of 1,3-butadiene from other C.sub.4 hydrocarbons, particularly monoolefins. U.S. Pat. Nos. 3,311,671 to Baker and 3,992,471 to Priegnitz teach the use of alkali metal-aluminum silicates on zeolites in effecting that separation. U.S. Pat. No. 3,596,436 to Dassesse discloses the use of activated charcoal to separate diolefins from monoolefins, but requires that the entire process be carried out in the vapor phase and provides for the regeneration of the solid adsorbent (removal of diolefins) with superheated steam. There is also separation art dealing specifically with the separation of isoprene from C.sub.5 hydrocarbon streams utilizing such methods as distillation, extractive distillation, liquid-liquid extraction and chemical treatment. Typical of such procedures is that shown in U.S. Pat. No. 3,851,010 and 3,947,506 which use distillations and extraction to recover high purity isoprene.
In contradistinction to the prior art, the present invention achieves the separation of isoprene from specific C.sub.4 and C.sub.5 hydrocarbons using an activated carbon or molecular sieve carbon adsorbent.